During operation, telecommunication equipment requires timing synchronization for proper communication purposes. Traditional synchronization methods utilize expensive specialized circuits to provide synchronization signals. Currently, with the prevalence of packet networks, such as, for example, Ethernet, cost can be reduced for timing synchronization by transmitting timing synchronization signals between telecommunication equipment within the packet network. However, due to the store-and-forward operation of packet networks, the synchronization signals or messages will experience an uncertain delay, which will affect the accuracy of synchronization. This uncertainty in delay is commonly referred to as packet delay variation (PDV). To improve timing synchronization accuracy, it is necessary for such delay to be significantly reduced or eliminated.
There are two known categories of methods for providing timing synchronization with reduced PDV. These categories include probabilistic filtering algorithms and long time averaging.
A probabilistic filtering algorithm filters out any large packet delays and uses the small packet delays for calculation of correction factors and timing synchronization of a local clock of a receive node with a transmit clock of a transmit node. This method usually has high complexity. The process of obtaining satisfactory small delays for calculation is random, therefore, successful performance of the probabilistic filtering algorithms in the short-term is not guaranteed.
In a second category, long time averaging provides a method that averages the delay of multiple transferred packets in order to eliminate the PDV. However, in an actual system, obtaining an absolute time is difficult because the local clock of the receive node is not accurate and requires synchronization. Any adjustment of the local clock may adversely affect the result of the delay averaging. Moreover, this method is not flexible, in that the result of the averaging cannot be controlled.